now..... we're assuming here, that the farmer planted "more than 35 acres" of corn, so, he planted some amount of corn, but he only harvested a fraction of it, which is 35 acres, and we're assuming he gave those 35 acres of harvested corn to the livestock, so the animals ate 1/8 of the corn he planted.
That means, if the animals ate 1/8 of the corn, and the farmer gave the animals the whole of the harvested corn, then we can say that the 35 acres is just 1/8 of what he planted.
now, if 35 is 1/8, what is the whole? namely 8/8?
[tex]\bf \begin{array}{ccll}
\stackrel{corn}{amount}&\stackrel{corn}{fraction}\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
35&\frac{1}{8}\\\\
c&\frac{8}{8}
\end{array}\implies \cfrac{35}{c}=\cfrac{\quad \frac{1}{8}\quad }{\frac{8}{8}}\implies \cfrac{35}{c}=\cfrac{1}{8}\cdot \cfrac{8}{8}
\\\\\\
\cfrac{35}{c}=\cfrac{1}{8}\implies 280=c[/tex]